using System;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(isStacked(11));

    }

​

    public static bool isStacked(int input)

    {

        int sum = 0;

        for (int i = 0; i <= input; i++)

        {

            sum += i;

            if(sum == input) return true;

        }

​

        return false;

    }

}